The Quark Theory
Introduction Over the years of physicists exploring the anatomy of the nucleus, a host of particles were discovered. The function of these exhumed particles were "largely unknown". A number of theories were developed in attempt to explain the existance of these particles. One of the most successful models to explain the particles' existance is the Standard Model. The Standard Model The Standard Model assumes that four fundamental interactions operate in the universe. These four fundamental interactions, also known as fundamental forces, are electromagnetic, weak, strong, and gravitational. The Standard Model identifies its behavior and relationships with the electromagnetic, strong, and weak interactions. Strong Interaction Strong interaction is the force that holds the protons and neutrons together in an atom's nucleus. Weak Interaction Weak interaction is a force present in the nucleus of an atom during radioactive decay. The weak nuclear force is the explanation to the decay of neutrons into protons and protons into neutrons. Attempts to prove the gravitational force as a medium of interaction in The Standard Model has not been successful. In addition to the fundamental interaction there are fundamental particles, known as quarks, which are theorized by physicists to make up the matter of protonshttp://en.wikipedia.org/wiki/Proton, neutronshttp://en.wikipedia.org/wiki/Neutron, and other nuclear particles. Quarks Quarks have fractional element charges. There are six identified variaties of quarks: The Up and Down Quarks The Up and Down quarks are the most common quarks and weigh the least out of all six flavors. They are identified as making up most ordinary matter, such as protons and nuetrons. The Strange Quark Just like a typical science-tale, the strange quark was discovered out of complete "strangeness". During a study of cosmic ray interactions, in 1947, a product of a proton collision with a nucleus was found to live for a much longer time than what was hypothesized. The product of the collision was expected to last 10-10 seconds when it lasted 10-23 seconds. This product was introduced as the lambda particle(Λ0)and the property which caused its unprecedented result was titled "strangeness". Since the strangeness property produced the lambda particle (Λ0), the additional unidentified quark that is the foundation of the lambda, baryon particle, in addition to the already classifed Up and Down quarks, was declared The Strange Quark. The longer lifetime of the study's result helped develop a new conservation law for such decays called the "Conservation of Strangeness". Particle decay by the strong or electromagnetic interactions preserve the strangeness quantum number (S=-1). The decay process of the lambda particle violates this rule. Since there is no lighter particle which contains a strange quark, the strange quark must be transformed to another quark present in the process. This tranformation can only occur by the weak interaction, which leads the particle to live a much longer lifetime. The Charm Quark Originally discovered as the J/Psi Particle (a meson) in 1974, this newly founded quark had over three times the mass of a proton, weighing in at about 3100 MeV. This particle decayed slowly and did not fit into the framwork of the up, down and strange quarks. This particle became the first firm experimental evidence for the fourth quark, the Charm Quark. Other particles that contain a charm quark are the D meson and a baryon particle called the lambda with the symbol Λ+c. *The D meson is the least massive meson which contains a charm quark. It provides unique examples of decay since the charm quark must be transformed into a strange quark by the weak interaction in order for it to decay. *The lambda with Λ+chttp://hyperphysics.phy-astr.gsu.edu/hbase/particles/lambda.html#c1particle weighs in at 2281 MeV/c2. The Bottom Quark In 1977, an experimental group from Fermilab discovered quark-antiquark pair at 9.4 GeV/c2, which was interpreted at the bottom-antibottom quark and was called the Upsilon Meson. The Upsilon particle was the first evidence of the existance of the fifth quark from the 1977 Fermilab experiment. From this experiment, the mass of the bottom quark results to be about 5 GeV/c2. The Top Quark In Apirl 1995, evidence of the existance of the Top Quark was proven. The evidence was found in the collision products of 9.0 TeV protons with equally energetic antiprotons (antiquarks are explained in section 5) in the proton-antiproton collider. The evidence involved analyzing trillions of proton-antiproton collisions. These trillions of proton-antiproton collisions were categorized into two groups. The first group is known as the Collider Detector Facility group and the second group is the D-0 group. As shown below, each group at a detector where these collisions were studied and classified. The Collider Detector Facility: IMG:http://i6.photobucket.com/albums/y207/kitty212kat/3eac5e74.jpg The D-0: IMG:http://i6.photobucket.com/albums/y207/kitty212kat/9fefe9b9.gif The value of the Top Quark mass is from the combined data of the two groups, weighing in at 174.3 +/- 5.1 GeV. This is over 180 times the mass of a proton. Each quark name identifies with its property. Each property is known as a flavor. Below is the table of all six quark properties and their charges. The energies listed above are used by physicists to determine the charge of a subatomic particle, such as a proton or a neutron. The energies needed to reduce subatomic particles into their referenced quarks are so high that the charge values of these quarks cannot be isolated as separate particles. Their existance can only be demonstrated by indirect means. The masses lisited in the table should not be taken too seriously because of the incapablity to isolate one quark directly, each quark's mass vary. The Quark Theory is an idea that demonstrates the matter of subatomic particles. Scientists today continue to search for the measurements of the undefined quark values and whether they represent the ultimate structure of matter or if there are even smaller subunits of measure. Practice Problems Using the Quark Table, one can calculate the quark structure of a subatomic particle. Quarks are observed to occur in combinations of two quarks (mesons), three quarks (baryons), and five quarks (pentaquarks). Below is a diagram of subatomic particles in the process of radioactive decay, illustrating the structure of the proton and neutron quark structures (two bayrons) transforming into a pentaquark through the medium of the strong interaction.: IMG:http://i6.photobucket.com/albums/y207/kitty212kat/87a5bfbf.gif 1. A proton has the structure uud (Up + Up + Down). Referencing the Quark Table, one obtains the charge value of Up= +⅔ e, and the charge value of Down= −⅓ e. IMG:http://i6.photobucket.com/albums/y207/kitty212kat/pro.jpg Proton= uud= e)+(+⅔ e)+(−⅓ e)= 1 e 2. A neutron has the stucture udd (Up + Down + Down). IMG:http://i6.photobucket.com/albums/y207/kitty212kat/nue.jpg Neutron= udd= e)+(−⅓ e)+(−⅓ e)= 0 e 3. A lambda+C is a baryon particle that has a composition of udc (Up + Down + Charm). IMG:http://i6.photobucket.com/albums/y207/kitty212kat/lam.jpg Lambda+C= udc= e)+(−⅓ e)+(+⅔ e)= 1 e The Antiquark Just like love and marriage, quarks do not exist alone. They are bound in quark-antiquark pairs or triplets by the strong force. Every quark carries some charge and its antiquark carries the opposite valued-charge that the quark maintains. However, for charge zero mesons with different types of quarks and antiquarks, there is an antiparticle that reverses the role and quark and antiquark. For example, the K0 meson (its charge value is 0) is made up of the down quark but its antiquark is the antistrange quark or the combination of a strange quark and an antidown quark. Charge zero mesons with the same types of quarks and antiquarks have the identical quark and antiquark pairs such as the Up Quark in a proton is paired with an Antiup quark. The explanation of the quark-antiquark pair proves the existance of Quarks. A free quark is not observed because by the time the separation is on an observable scale, the energy is far above the pair production energy for quark-antiquark pairs. The energy required to separate them produces quark-antiquark pairs long before they are far enough apart to observe separately. Bibliography References *(CDF Image) http://hyperphysics.phy-astr.gsu.edu/hbase/particles/fermidet.html#c1 *(D 0 Image) http://hyperphysics.phy-astr.gsu.edu/hbase/particles/fermidet.html#c2 *Fermilab http://hyperphysics.phy-astr.gsu.edu/hbase/particles/accel.html#c2 *(Pentaquark diagram)http://hyperphysics.phy-astr.gsu.edu/hbase/particles/pquark.html#c1 *(Practice Problems: 1. and 2.) Barron’s Review Course Series: Let’s Review Physics; pg 483 *(Quark Table: Flavor and Charges) Barron’s Review Course Series: Let’s Review Physics; pg 483 *(Quark Table: Masses) http://hyperphysics.phy-astr.gsu.edu/hbase/particles/quark.html Resources *Fermilab http://hyperphysics.phy-astr.gsu.edu/hbase/particles/accel.html#c2 *Hyper Physicshttp://hyperphysics.phy-astr.gsu.edu/hbase/particles/quark.html#c3 *Keith, Michael. "Quarks and Antiquarks." Egglescliffe Physics Website. 2001. Egglescliffe Physics. 11 Jun 2006 . *Lazar, Miriam A.Barron's Review Course Series; Let's Review: Physics. 3rd. Hauppauge, NY: Barron's Educational Series, Inc., 2004. *Quinn, "Theory Antiparticles." 2003. 11 Jun 2006 . *Zitzewitz, Paul W. PHYSICS: Princliples and Problems. New York, NY: Glencoe McGraw-Hill, 1999.